This study will attempt to develop a sensitive double antibody radioimmunoassay to quantitate IgE production in vitro by peripheral blood lymphocytes. In parallel with this aspect of the study, peripheral blood lymphocytes will be fractionated into subpopulations on the basis of surface receptors. The T cell population will be further fractionated into subpopulations with surface receptors for the Fc portion of IgG or IgM, for histamine and for theophylline. The study will attempt to ascertain what effect, if any, these T cell subpopulations exert on the production of IgE in vitro.